Dry powdered pesticide compositions are known which include a diluent, wetting and dispersing agents, penetrating agents, foam stabilizers, couplers, and a variety of other materials to enhance the stability of the pesticide and improve the salability of the composition. A number of pesticides, however, are unstable in the dry powdered form due to sensitivity to moisture.
Attempts to solve the instability of such pesticides to moisture have centered on provision of a water scavenger or moisture barrier compound or combination thereof. In years past, the selection of a suitable water scavenger or mixture of scavengers was made readily by one skilled in the art in accordance with known principles and properties as set forth in various journals and publications by the suppliers of such materials, and in reference works such as McCutcheon's Handbook, Volume 1: Emulsifiers and Detergents (1991 North American Ed., McCutcheon Division, MC Publishing Co.) and in McCutcheon's Handbook, Volume 2: Functional Materials (1992 North American Ed., McCutcheon Division, MC Publishing Co.).
Epichlorohydrin was the best known scavenger available for many years. This compound was found to be acceptable by EPA for use in pesticide formulations and was permitted for use on growing crops. It has recently been ruled, however, that epichlorohydrin can no longer be used for formulae applied directly to growing crops.
Chemists have been searching for scavengers that are useful in bonding the free moisture in dry pesticide formulations and thus preventing the moisture from coming into contact with the pesticide. Such scavengers are desired to minimize decomposition of the pesticide and extend the shelf life of the product so that the product becomes commercially feasible. A number of different approaches to solving the problem of rapid degradation of the pesticide by small amounts of moisture have been attempted.
It has been proposed to use various types of surfactants. Nonionic surfactants such as those developed and marketed in the industry as alkylphenoxy polyethoxy ethanols, or those generally described as octyl or nonylphenol hydrophobes, have been suggested. Examples of such materials include adducts of 8 to 10 moles of ethylene oxide with octyl or nonyl phenol.
Use of anionic surfactants has also been considered. One exemplary anionic surfactant is sodium lauryl sulfate, which is also useful as a wetting agent which is required to wet the powder in the spray water as well as wet the leaf surfaces to which the pesticide composition is to be applied. It was believed that this type of chemistry would be helpful in bonding the free moisture in the formulae.
However, none of the known surfactants have proven useful as moisture barriers or scavengers for dry pesticide compositions.
Solvents such as alcohols, propylene glycol, ethylene glycol butyl ether, butyrolactone and tetrahydrofurfuryl alcohol have been possible candidates as moisture scavengers since they also have the ability to hold and bond water. However, the flammability of these solvents would make powdered products dangerous to manufacture and store.
It would be desirable to provide a dry pesticide composition which is stabilized against degradation due to contact with moisture. The composition desirably would include a stabilizer which is environmentally friendly, safe to use and store, and compatible with the pesticides with which it is combined in the dry composition.